This invention concerns a tunnel system for a hot strip rolling mill linked to the continuous casting of thin slabs.
To be more exact, this invention concerns a tunnel system for the storage and temperature equalization of the slabs, the system being positioned between two twin lines for the continuous casting of thin slabs and the strip rolling line.
The present applicants are not aware of the existence of tunnel systems according to this invention.
According to the invention a first insulated tunnel is included downstream of each of two lines for the continuous casting of thin slabs. Slabs of a slender thickness coming from the respective continuous casting line arrive in this insulated tunnel after having been inspected and sheared to size.
The spirit of the invention covers processing with two casting lines in sequence in such a way as to create a desired interval, of about half the length of the thin slab for instance, between the leading end of one thin slab coming from one casting line and the leading end of another thin slab coming from the other casting line.
A temperature-equalization furnace tunnel for each continuous casting line is located between the insulated tunnels and the strip rolling train and ensures perfect equalization of the temperature of the thin slab.
The system (insulated tunnels and temperature-equalization tunnel), in the event of stoppages of the strip rolling train, enables a stock to be built up consisting of a number of slabs equal to the quantity of liquid steel contained in the ladle.
Each chamber of the insulated tunnels contains a determined number of powered roller conveyors positioned one above another and borne on a framework capable of vertical movement so that the roller conveyors can be aligned with the respective upstream roller conveyor of the casting line and with the respective downstream roller conveyor of the temperature-equalization furnace tunnel.
These storage roller conveyors are advantageously positioned above the working roller conveyor.
The two temperature-equalization furnace tunnels consist substantially of one single body containing two independent side-by-side chambers, one per each casting line, within which are included powered rollers that feed the thin slab towards the rolling mill.
Suitable burners positioned above and possibly also below the thin slab and divided into temperature-adjustment zones ensure perfect equalization of the temperature of the thin slab during its movement of feed.
Both the side-by-side chambers can move transversely to enable their axes to be aligned alternately with the axis of the rolling mill.
Under normal working conditions the thin slabs coming from the two continuous casting lines pass into their respective insulated tunnels, then into the chambers of the temperature-equalization furnace tunnels and thence alternately into the hot strip rolling mill.
When a slab is positioned in its respective temperature-equalization tunnel, the invention includes the possibility of halting the slab for enough time for every part of the slab to have the required temperature in a uniform manner. Such halting of the slab enables the heating and temperature-equalization curve to be checked accurately.
If ever it is necessary to halt the rolling mill, it is possible to build up a stock of a number of thin slabs corresponding to the weight of the steel held in the ladle and to arrange these slabs on appropriate tiers of rollers in the insulated tunnels, these tiers descending in sequence until storage has been completed.
When the rolling mill starts up again, the thin slabs are fed forwards from the roller conveyors of the insulated tunnels to the chambers of the temperature-equalization furnace tunnels until the two insulated tunnels have resumed their intial condition.
When it is necessary to feed cold, stored, thin slabs to the rolling mill, according to a variant the invention comprises a heating furnace, which raises the temperature of the slabs to about 900.degree. C. and is followed by one of the two temperature-equalization furnace tunnels, which enables the thin slab to be heated to the rolling temperature. This temperature-equalization furnace tunnel is positioned momentarily in cooperation with the outlet of the heating furnace.
According to a variant an emergency flying shears is included at the outlet of the temperature-equalization furnace tunnel and starts working by shearing the thin slab arriving, in the event of the rolling mill being obstructed.
According to a further variant a descaling assembly is provided at the inlet of the rolling mill so as to remove the scale formed on the surface of the slab during heating; the descaling assembly is followed by a vertical stand suitable to gauge the sides of the slab.
Yet another variant consists in introducing between the insulated tunnel and the temperature-equalization tunnel a further induction-heating furnace so as to create the following situation.
The insulated tunnel is able to ensure the maintaining of the temperature of the slab, the induction-heating furnace can ensure that the heating of the slab is kept homogeneous and the temperature-equalization furnace tunnel can ensure equalization of the temperature throughout the slab.